Induction is defined as the legitimate inference of the more general, from the less general;—the general from the particular;—and (with more startling distinctness) of the Unknown from the Known. It is at once evident that, whatever may be the logical form into which this mode of inferring is thrown, there must in the nature of things be some ulterior principle to give it legitimacy. This principle, when raised to the rank and dignity of a philosophic postulate, is commonly known as the Law of Natural Uniformity. A law claiming such extensive dominion that one cannot help asking in what code, human or Divine, of reason or of experience, it was originally found written.
Let us have recourse to the code of reason first. Euclid gives admirable instances of things true by necessity of reason. The moment we understand what right lines are, we see at once and for all time that two straight lines, infinitely prolonged, can never inclose a space. No one ever did see a mathematical line of any kind ("length without thickness"),—no one ever saw or conceived any real or ideal thing of infinite extent, neither can we think infinity at all. Yet the terms of the geometrical proposition carry their own evidence. We may sum the case, as Euler the mathematician put it. He finished a demonstration upon Arches by saying, "All experience is contrary to this, but that is no reason for doubting its truth."
Now, there appears nothing in the least resembling this case, in the conception of Natural Uniformity. No thinker can predicate substantial impossibility of the idea that Nature should ever be otherwise than Uniform.
Suppose, then, we consider the code of Experience. Where shall we find the experience required? Ours is far short of universal, either in an absolute or an approximate sense. We are the children of to-day—yet the law wanted must be to all intents universal. It has been answered to this obvious requirement, that we enjoy the results of an experience constant and uniform, "coextensive not with the life of the single individual who employs them, but with the entire history of the human race."[154] But in what history is any such experience written? History in its letter, is full of events which contradict Nature's uniformity, of interruptions, marvels, miracles. For cattle to speak, is quite a common occurrence in Livy. An ordinary Roman would have been perplexed by the absence of signs and wonders; he would have felt it something to be accounted for. History tells us on every written page to believe in what seems impossible; and some writers on historical evidence, claim for it a greater amount of credibility whenever it testifies to the greater number of improbable incidents. For, do not writers of fiction deal in probabilities?[155]
Another method of giving force to the principle of natural Uniformity, is based on our alleged sense of personal subjection to the chain of events;—the outer world is said to penetrate the inner by an impression of its unvarying sequence, its laws of unbroken continuity. But does the lesson of life really go this way? Most men, when meditating over their own lives, think rather of the causation they have themselves exercised, or might have exercised, than of any iron links of causality in nature. So strongly do they feel their causal power, that, whereas one man boasts of being the architect of his own fortunes, another blames himself because he has been foolish enough to let things take their chance. What people chiefly realize and act upon, is the relation between Man and Nature—or, else between Man and Man;—relations prolific in consequences which we shall have to consider by-and-bye.
A more summary mode of explaining our human impression of natural Uniformity, is by resolving it into certain laws of Association. We see antecedent and consequent every day, and get to consider them as indissolubly associated. If we see a present antecedent, we expect a coming consequent. The event and its futurity, are thus fused in a common solvent. Yet, one palpable objection lies against this theory, and it is fatal. Fatal against it, and against all theories which rest our belief upon experience, or upon any process of reasoning, inductive or demonstrated. The objection consists in the plain fact, that this belief resembles animal instinct[156] in one definite particular—it exists previously to all observation or exercise of intelligence on the subject.
We see it in all young creatures. The instinct of children is to act upon a supposition that the thing they have enjoyed or suffered shall recur regularly and without interruption. The darling brought down to dessert every day for a week, feels injured by a breach of the custom, just as the cat or dog fed from their masters' table expects the same hand to continue always kind. Child, kitten, and puppy, need no second scalding to look askance at the tea-kettle. Grown people's confidence in the stability of Empires often reposes on no much stronger foundation. Most men rest satisfied with an indefinite and unreasoning presumption all their lives long. They desire no further explanation—a happy circumstance, perhaps, considering the theories they might have to investigate.
Mr. James Mill in his "Analysis of the Human Mind" made great and continual use of the laws of Association. He applied them (amongst other ways) to our belief in the uniform futurities of Nature. "There can" he writes "be no idea of the Future; because strictly speaking the Future is a non-entity—of nothing there can be no idea.... Our whole lives are but a series of changes, that is, of antecedents and consequents. The conjunction, therefore, is incessant; and, of course, the union of the ideas perfectly inseparable." (Vol. I. pp. 362-3.) And again, (p. 367,) "But I am told, that we have not only the idea of to-morrow, but the belief of to-morrow; and I am asked what that belief is. I answer, that you have not only the idea of to-morrow, but have it inseparably. It will also appear, that wherever the name belief is applied, there is a case of the indissoluble association of ideas. It will further appear, that, in instances without number, the name belief is applied to a mere case of indissoluble association; and no instance can be adduced in which anything besides an indissoluble association can be shewn in belief. It would seem to follow from this, with abundant evidence, that the whole of my notion of to-morrow, belief included, is nothing but a case of the inevitable sequence of ideas."—This theory Mr. Bain (no hostile critic) annotates as follows. "The case that is most thoroughly opposed to the theory of indissoluble association is our belief in the Uniformity of Nature. Our overweening tendency to anticipate the future from the past is shown prior to all association; the first effect of experience is to abridge and modify a strong primitive urgency. There is, no doubt, a certain stage when association co-operates to justify the believing state. After our headlong instinct has, by a series of reverses, been humbled and toned down, and after we have discovered that the Uniformity, at first imposed by the mind upon everything, applies to some things and not to others, we are confirmed by our experience in the cases where the uniformity prevails; and the intellectual growth of association counts for a small part of the believing impetus. Still, the efficacy of experience is perhaps negative rather than positive; it saves, in certain cases, the primitive force of anticipation from the attacks made upon it in the other cases where it is contradicted by the facts. It does not make belief, it conserves a pre-existing belief." In Mr. Bain's comment it is worthy of particular remark that he considers experience less as a foundation, than a test always,—a limit sometimes,—of that law which gives life to all the experimental sciences. "The uniformity imposed by the mind," he observes, "applies to some things but not to others." His view, therefore, places the principle itself in the light of a generality given by the mind and apprehended as a leading maxim. Its field is sometimes reasserted,—sometimes contracted,—by experience; but in both cases the effect is a process of discrimination.